The present invention relates to photonic network technology, and more particularly to an optical communication apparatus, an optical communication system, and a path control method for switching paths between nodes.
In recent years, various technologies relating to a photonic network have been developed.
For example, Patent Literature 1, Patent Literature 2, and Non-Patent Literature 1 disclose some photonic network technology.
Patent Literature 1 discloses a drop circuit and an add circuit used in a reconfigurable optical add/drop multiplexer (ROADM device). Furthermore, Patent Literature 1 describes a colorless function using a wavelength selective switch (WSS). Patent Literature 1 also describes a direction function of switching paths to a different path with use of a wavelength cross connect device (WXC).
Similarly, Patent Literature 2 discloses a colorless function, a direction function, a wavelength cross connect device, a wavelength selective switch, and the like.
Furthermore, high-speed communication for 40 Gb/s or 100 Gb/s has been available in a digital optical transmission technology by using a phase modulating technique and a coherent receiving technique. For example, Non-Patent Literature 1 discloses such related technology.
For example, it is assumed that four nodes (Nd=4) are connected using ROADM devices having no colorless function or directionless function as shown in FIG. 16.
In this network, a path of a channel λ1 currently connected is to be switched into a different path (ROADM1→>ROADM4→ROADM3) using a channel λ2 (see FIG. 17).
In this case, there are required operations of preparing a new transponder TPND1-2 on ROADM1 of FIG. 17, opening a path of λ2, and finally changing a client. This is because the wavelength that can be transmitted to a connection port of a transponder is fixed if a ROADM device has no colorless function.
Even a ROADM device that copes with a colorless function needs to be connected to an add/drop part connected to a different path if it does not cope with a directionless function.
In order to switch optical transmission paths and channels (i.e., light wavelengths) of an optical communication apparatus that does not cope with a colorless function, an operator needs to go to an instillation site of a node and to directly rearrange an optical fiber into a connection terminal for a wavelength to be switched. This is because a remote operation cannot be performed since the channel of a ROADM device is fixed for a connection terminal of a transponder. At that time, an alternative transponder should be prepared in some cases. Such an operation arises problems requiring various costs such as cost of sending an operator, employment cost, facility cost, and cost of making a work planning. Furthermore, the downtime becomes longer along with a period of time required for such an operation. Thus, various problems will arise.
Even a ROADM device that copes with a colorless function suffers from signal interruption during a switching period of the ROADM device. In other words, primary signals cannot be transmitted during an operation of switching paths of a ROADM device (signal interruption period). Thus, transmission efficiency is problematically lowered.
When paths are to be switched, channels change from a current one in some cases where, for example, signals using the same channel (wavelength) have already been transmitted on a new path. In such cases, a new path should be ensured by changing not only transmission paths, but also channels.
In the field relating to the present invention, it has been desired to be capable of coping with various functions that will be provided in the near future. For example, the amount of communication data flowing through optical networks may greatly vary in a day or several hours depending upon a variety of social activities (sports or musical events, incidents, accidents, and the like). As a countermeasure for such variations, therefore, operations of switching paths in an optical communication apparatus may be performed per day or a shorter period.    Patent Literature 1: JP-A 2010-098545    Patent Literature 2: JP-A 2009-212584    Non-Patent Literature 1: Thesis “Performance of Dual-Polarization QPSK for Optical transport systems,” Kim Roberts, Maurice O'Sullivan, Kuang-Tsan Wu, Han Sun, Ahmed Awadalla, David J. Krause, and Charles Laperle, Journal of Lightwave technology, vol. 27. No. 6, 2009